1. Field of the Invention
The present invention relates to a method for preparing a ferroelectric semiconductive coating and to an apparatus for removing environmental air pollutants using this coating and electric power. More particularly, the present invention relates to an air cleaning apparatus which utilizes a ferroelectric semiconductor coated with a metal. The air cleaning reaction device can be used for air cleaning within a room or in industrial areas where noxious gases are generated. The apparatus and the method have various advantages such as cost reduction by using electric power as an energy source, increased efficiency, light weight, simplicity, a rapid treatment for large volumes of air, and improved safety.
2. Description of the Related Art
As well known, a large number of air cleaners are available, most of which utilize a filter. However, although these air cleaners can remove foreign materials such as dust, they fail to completely remove air pollutants which are fine particles or gases, for example, noxious gases, gases containing heavy metals, etc. Therefore, advanced types of air cleaners employ a plasma generator or an electron beam generator to burn the air pollutants. However, even these advanced types of air cleaners do not completely clean the polluted air.
Another air cleaner utilizes titanium oxide as a semiconductive material catalyst. Heat is applied to the catalyst to cause adsorption and dissolution of noxious organic compounds and non-combustion hydrocarbon compounds on the catalyst. However, applying heat to cause catalytic combustion leads to the following problems: the area occupied by the apparatus is extremely large; and the energy cost is high.
If semiconductive materials absorb energy exceeding the energy band gap, conduction electrons in the semiconductive material are excited and move from a valence band to a conduction band. Positive holes are left in the valence band, and electrons are excited into the conduction band, thereby forming electron-hole pairs. At this time, the behavior of the electron-hole pairs of the semiconductor, to which an electric field is applied, prolongs the moving life of a carrier to delay re-coupling, and the produced electron-hole pairs join in a reaction with the compounds.
In such semiconductive materials, the titanium oxide having a negative ion lack type of nonstoichiometric shear structure is an effective material that can be employed as a catalyst, and if it absorbs the band gap energy of 3.2 electron volts or more and/or light having 250-400 nanometer wavelengths, the conduction electrons are excited, thereby forming the electron-hole pairs. The excited titanium oxide itself does not dissolve. The positive holes produce an OH radical as a strong oxidizing agent, thereby decomposing polluted materials through an oxidation reaction. The electrons are utilized for the reduction reaction.
Therefore, the titanium oxide as the photo-catalyst adsorbs noxious organic materials, non-combustion hydrocarbon compounds, etc. contained in the air or water to decompose the adsorbed contents into the following state equation: catalyst/band gap energy:       Catalyst          BandGapEnergy      :      Ebg         greater than             CO      2        +                  H        2            ⁢      O        +          Mineral      ⁢              xe2x80x83            ⁢              Acids        .            
Also, the titanium oxide catalyst has characteristics suitable for reactions such as, sterilization and antibiosis, burning removal and deodorization of odor, hot wave reflection, cigarette nicotine decomposition and removal, self-cleaning, and oil decomposition and therefore, has already been put into practical use in various industrial fields.
In order to induce an appropriate reaction, a conventional air cleaning apparatus is generally subjected to ultraviolet irradiation to supply the band gap energy. However, upon ultraviolet irradiation the catalytic reaction is exhibited only on the section of the semiconductor where light is absorbed. Efficiency is low due to the straightness, reflection, and refraction of the light.
Therefore, the conventional air cleaning apparatus has numerous limitations when applied to various industrial spots. For example, due to various kinds of restrictions such as the problem of installing a light source, the thickness of the optical catalyst coating, environmental factors in placing the installation, installation cost, structural problems and so on, the conventional air cleaning apparatus is not widely applied in industrial areas, even though it is effective in catalyzing the decomposition reactions.
It is, therefore, an object of the present invention to provide a method for preparing a ferroelectric semiconductive coating which is capable of bonding with a metal and which is capable of forming electron-hole pairs on the surface of the ferroelectric semiconductor with 440 V and 30K-100K Hz alternating current (AC) electric energy having high voltage and high frequency as an energy source, based upon the energy level difference between the semiconductor and the metal, whereby it can exhibit an effective surface reaction in the range of the oxidation and reduction reactions even in an enclosed space where no ultraviolet irradiation occurs.
It is another object of the present invention to provide a ferroelectric semiconductive coating capable of achieving a light weight and simplicity of the structure and carrying out rapid treatment for a large volume of air.
It is still another object of the present invention to provide a method for preparing a ferroelectric semiconductive coating on a metal material, applying electric power generated by the application of an alternating current (AC) voltage to the metal material and the ferroelectric semiconductive coating, and to provide an apparatus for removing environmental air pollutants using the coating and electric power.